Transistors, such as bipolar transistors, MOSFET or IGBT, are widely used as switches for switching electric loads, such as electric motors or electric lighting, or as switches for generating an oscillating voltage from a DC input voltage in a switched-mode power supply. In those applications it is often required to measure a current through the transistor.
MOS-Transistors are voltage-controlled components that can be switched on and off using a drive voltage which is, for example, in the range of several volts, while—depending on their specification—they are capable of switching load voltages of up to several hundred volts. Usually a drive voltage for a transistor is provided by a drive circuit that receives a supply voltage which is high enough for the drive circuit to generate the drive voltage. In some applications, such as, for example, some types of switched-mode power supplies, the supply voltage is generated when the load transistor is cyclically switched on and off. In these cases, however, a start-up circuit is required that provides the supply voltage before the load transistor is switched on for the first time.
There is, therefore, a need for providing an electronic circuit with a load transistor that has a current sense and a start-up capability.